As one of the first genetic conditions for which community carrier screening is possible, cystic fibrosis provides an opportunity to examine the way in which health professionals understand and assess issues associated with the clinical applications of the `new genetics'. This paper presents the results of a postal survey of general practitioners in the UK. Completed questionnaires were returned by 388 GPs (64%). The majority had a limited understanding of the epidemiology and population genetics of CF. Less than half (164, 44%) indicated the correct estimate of carrier frequency and only a third (144, 39%) indicated the correct likelihood of inheriting the carrier state. By contrast, the majority of GPs supported community carrier screening for CF. Almost all (339, 92%) felt the benefits of screening were important, and almost half (172, 45%) wanted to offer carrier screening in their own practices. These findings point to major gaps in GPs' understanding of genetics and raise further questions about the grounds on which their support for screening is based.